The present invention relates to centrifugal pumps, and in particular, pumps of this type that have a chopping or cutting capability.
A variety of centrifugal pumps are known currently which are capable of pumping liquids and slurries containing solid matter such as small pieces of garbage or other disposed items. These pumps have the capability of chopping or cutting solid matter in the liquid mixture permitting the output from the pump to be disposed of more readily.
U.S. Pat. No. 3,155,046 issued Nov. 3, 1964 to James E. Vaughan describes a centrifugal pump for pumping a mixture of liquid and stringy solid material that includes a housing with a peripheral wall having a discharge aperture therein, a closed end, and an open end. The pump has an impeller secured on a shaft and the impeller has radially disposed impeller blades. Edges of these vanes adjacent to the pump inlet co-operate with sharpened edges of pump inlet apertures to cut solid material entering the pump.
One pump known in the prior art is the ABS "Piranha" Grinder pump. This pump incorporates sharpened spiral cutting grooves on the inside of an intake plate of the pump. Front edges on the impeller vanes of the pump rotate against the grooves to produce a cutting action. The edges of the vanes are flat in profile. This pump design is susceptible to binding problems from material being wedged between the impeller edges and the intake plate.
Another known pump is the Vaughan chopper pump disclosed in U.S. Pat. No. 5,256,032 issued Oct. 26, 1993. Features to chop and expel material from behind the impeller of the pump are incorporated into the design. The pump incorporates elongated curved vanes of the impeller operating in close cutting relationship with axially protruding ribs on a back plate of the casing. The vanes of the pump produce a cutting action as they pass over the ribs on the back plate.
Yet another known centrifugal pump is the screw centrifugal pump which utilizes spiral grooves in the rear face of the impeller of the pump and on the back plate of the casing of the pump. The rotating groove in the rear of the impeller operates against the stationary grooves in the casing backplate providing the function of discharging solids from the space between the backplate and impeller of the pump.
A known Allis-Chalmers type "SSOR" pump designed especially for pumping paper stock in a paper mill employs an impeller that rotates in a pump casing having a frontal inlet and a side outlet. This known impeller has a partial back shroud and two vanes project forwardly from this back shroud. These vanes, which are twisted along their length, sweep backwardly from around a leading edge. This pump does not have any capability of chopping or cutting solids that enter the pump.
An object of the present invention is to provide a novel and durable centrifugal pump effective for pumping a mixture including solids suspended in a liquid.
A further object of the invention is to provide an efficient and reliable centrifugal pump having an improved impeller with radially extending vanes.
Preferably the present pump is provided with a radial partial back shroud with sharpened leading shroud edges that cooperate with grooves formed on a back plate of the pump casing. The sharpened shroud edges and the grooves interact to cut solids that have entered the pump through the intake port.